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The most severe injuries in the Boston bombing resemble those suffered by troops in Iraq and Afghanistan whose limbs were blown apart by improvised explosive devices —and the initial treatment was also identical: First responders — and in some instances, spectators — used tourniquets to cut off the blood flow and stop severe bleeding.

More than 170 people were hurt Monday and three people died when two explosive devices went off along mile 26 of the Boston Marathon on Boylston Street.

“A lot has emerged from the Iraq and Afghan wars,” adds Yaffe, who is a lieutenant colonel in the Army Reserve. “A tourniquet is a standard piece of equipment for a soldier to carry now. They might wear one out on an assignment and not tighten it unless they have to.”

Tourniquets have been used in war for hundreds of years; they’ve been carried by every U.S. service member in combat since 2006, with an estimated 3,000 lives saved.

To make a tourniquet, a strip or band of cloth is wrapped tightly around a bleeding arm or leg above the wound to compress the area and stem blood flow. Troops use a simple version with a Velcro strap that can be applied with one hand.

The Boston scene Monday was “numbingly reminiscent of some of the scenes we saw in Iraq and Afghanistan,” said retired Army Col. Brian Eastridge, a veteran of several combat deployments who directed trauma care in both war zones.

But tourniquets do pose a threat to the limb, and experts warn that they should be applied with caution.

While the thinking about when to apply a tourniquet is evolving, only trained people should use them or only as a last resort, according to Jeffrey Pellegrino, a member of the Scientific Advisory Council of the American Red Cross.

He said the limb below the tourniquet can be damaged when blood flow is cut off for too long and might have to be amputated. For that reason, tourniquets should also be marked with the time they were applied. After 30 minutes, he said, the tourniquet should be slowly loosened, but not removed, to allow some blood to flow to the wounded tissue below the strap.

“The majority of bleeding incidents can be stopped by applying direct pressure to the wound,” Pellegrino said. “That’s always the first thing someone applying first aid should do.”

Most people who take first aid training from the American Red Cross will not even learn about tourniquets because of the risk to the limb. It is taught by the American Red Cross in wilderness classes, however, for cases where someone can’t call 911 for help.

Bleeding from a trauma becomes “life threatening as the patient goes into shock. This typically occurs when more than 20 percent of a patient’s blood volume is lost,” said physician Jonas DeMuro, who works in the division of trauma and critical care at Winthrop-University Hospital in Mineola, N.Y.

But both in combat and in cases such as the Boston Marathon bombing, Yaffe said, the benefits of using a tourniquet can outweigh the risks.